The present invention relates to an ester elastomer having good flexibility and excellent mechanical characteristics at high temperature, particularly excellent creep resistance at high-temperature and a process for its production.
With the increased consciousness of ecology, the substitution of recyclable materials for conventional materials is progressing at an accelerated rate in various industries. Thermoplastic elastomers (TPE) have attracted attention as recyclable rubbery materials for many years but as the concept of eco-friendliness is given greater emphasis of late, those materials have come to be used more and more frequently in many applications in automotive and other industries.
Among thermoplastic elastomers, polyester elastomers (hereinafter referred to as TPEE) are outstanding in mechanical strength, heat resistance, wear resistance, and flexural fatigue resistance so that they are broadly used in various industries, particularly in automotive industry. However, TPEE has the disadvantage of (1) high hardness beyond the usual rubber hardness region and, hence, low flexibility and (2) large compressive set at large deformation and/or high temperature and consequent lack of creep resistance. As such, improvements in these aspects have been demanded.
In order to impart flexibility to TPEE, it is necessary to reduce the proportion of the hard segment component which is to shoulder physical crosslinking and a technology for decreasing the hard segment component has been proposed in Japanese Kokai Publication Hei-2-88632, for instance. However, the application of the technique leads to a reduction in the block property of the hard segment component, with the result that the melting point of the resin is depressed and the mechanical properties at high temperature are also sacrificed. With regard to creep resistance, too, a technology for increasing the degree of polymerization to improve the creep resistance has been disclosed in Japanese Kokai Publication Sho-52-121699, for instance, but the consequent improvements in mechanical characteristics are limited and it was also difficult to reconcile creep resistance with flexibility.
The present invention has for its object to provide an ester elastomer having a high block of the hard and soft segment components, high flexibility, and good mechanical properties at high temperature, particularly high temperature creep resistance and a process for producing said ester elastomer.
The present invention, in a first aspect, relates to an ester elastomer which comprises a block copolymer comprising a polyester copolymer (A) and a polymer having hydroxyl groups at both terminal ends (B) (hereinafter referred to sometimes as hydroxyl-terminated polymer) which are coupled to each other through the intermediary of an urethane component (C) containing a group of general formula (1);
xe2x80x94Oxe2x80x94COxe2x80x94NHxe2x80x94R1xe2x80x94NHxe2x80x94COxe2x80x94Oxe2x80x94xe2x80x83xe2x80x83(1)
(wherein R1 represents an alkylene group containing 2 to 15 carbon atoms, xe2x80x94C6H4xe2x80x94, xe2x80x94C6H4xe2x80x94CH2xe2x80x94, xe2x80x94C6H4xe2x80x94CH2xe2x80x94C6H4xe2x80x94 (where xe2x80x94C6H4xe2x80x94 represents phenylene)) and/or a group of general formula (2);
xe2x80x94Oxe2x80x94COxe2x80x94NHxe2x80x94R2xe2x80x94NHxe2x80x94COxe2x80x94xe2x80x83xe2x80x83(2)
(wherein R2 represents an alkylene group containing 2 to 15 carbon atoms, xe2x80x94C6H4xe2x80x94, xe2x80x94C6H4xe2x80x94CH2xe2x80x94 or xe2x80x94C6H4xe2x80x94CH2xe2x80x94C6H4xe2x80x94 (wherein xe2x80x94C6H4xe2x80x94 represents phenylene)),
where said polyester copolymer (A) consisting of 50 to 95 weight % of a short-chain polyester component (a1) comprising a group of general formula (3);
xe2x80x94COxe2x80x94R3xe2x80x94COxe2x80x94Oxe2x80x94R4xe2x80x94Oxe2x80x94xe2x80x83xe2x80x83(3)
(wherein R3 represents a bivalent aromatic hydrocarbon group containing 6 to 12 carbon atoms; R4 represents an alkylene group containing 2 to 8 carbon atoms) as a recurring unit and 50 to 5 weight % of a long-chain polyester component (a2) comprising a group of general formula (4);
xe2x80x94COxe2x80x94R5xe2x80x94COxe2x80x94Oxe2x80x94Lxe2x80x94xe2x80x83xe2x80x83(4)
(wherein R5 represents a bivalent aromatic hydrocarbon group containing 6 to 12 carbon atoms; L represents an oligomer component (L) having a glass transition temperature of not higher than 20xc2x0 C. and a number average molecular weight of 500 to 5000) as a recurring unit, said hydroxyl-terminated polymer (B) having a glass transition temperature of not higher than 20xc2x0 C., a number average molecular weight of 500 to 5000, and the absolute difference |xcex4B-xcex4L| [where xcex4B represents the solubility parameter of said hydroxyl-terminated polymer (B) and xcex4L represents the solubility parameter of said oligomer component (L) of said long-chain polyester component (a2)] being not greater than 0.5.
The present invention, in a second aspect, relates to a process for producing an ester elastomer which comprises melt kneading 100 parts by weight of the polyester copolymer (A) comprising 50 to 95 weight % of the short-chain polyester component (a1) and 50 to 5 weight % of the long-chain polyester component (a2), said long-chain polyester component (a2) containing the oligomer component (L) having a glass transition temperature of not higher than 20xc2x0 C. and a number average molecular weight of 500 to 5000, 50 to 500 parts by weight of the hydroxyl-terminated polymer (B) having a glass transition temperature of not higher than 20xc2x0 C. and a number average molecular weight of 500 to 5000, the absolute difference |xcex4B-xcex4L| ([where xcex4B represents the solubility parameter of said hydroxyl-terminated polymer (B) and xcex4L represents the solubility parameter of said oligomer component (L) of said long-chain polyester component (a2)] being not greater than 0.5, and 10 to 100 parts by weight of the isocyanate compound (Cxe2x80x2).
The present invention, in a third aspect, relates to an ester elastomer having a surface hardness of 60 to 90 and a 72-hour compressive set at 120xc2x0 C. of not greater than 90%.
The present invention is now described in detail.
Referring to the first aspect of the invention, the polyester copolymer (A) comprises of 50 to 95 weight % of a short-chain polyester component (a1) of the general formula (3) shown above and 50 to 5 weight % of a long-chain polyester component (a2) of the general formula (4) shown above.
The above polyester copolymer (A) generally consists of recurring units of short-chain polyester component (a1) and long-chain polyester component (a2).
In the above general formula (3) representing said short-chain polyester component (a1), R3 represents a bivalent aromatic hydrocarbon group containing 6 to 12 carbon atoms and R4 represents an alkylene group containing 2 to 8 carbon atoms.
Preferably said short-chain polyester component (a1) may for example be polybutylene terephthalate, polybutylene 2,6-naphthalate, or polyethylene 2,6-naphthalate, for those compounds contribute to the formation of ester elastomers having satisfactory creep resistance at high temperature. Particularly when polybutylene 2,6-naphthalate or polyethylene 2,6-naphthalate is used, a remarkable improvement is obtained in creep resistance at high temperature.
The long-chain polyester component (a2) is represented by general formula (4), and contains said oligomer component (L) having a glass transition temperature of not higher than 20xc2x0 C. and a number average molecular weight of 500 to 5000 as a constituent unit. In the above general formula (4), R5 represents a bivalent aromatic hydrocarbon group of 6 to 12 carbon atoms.
The oligomer component (L) mentioned above, when it exists as an independent substance, has hydroxyl groups at both termini thereof, and in the long-chain polyester component (a2), each of the two termini is in the form of an ester bond. This oligomer component (L) may for example be a polyether, aliphatic polyester, polylactone, polycarbonate, polyolefin, polybutadiene, polyisoprene, polyacrylate, polysiloxane, and other compounds which have hydroxyl groups at both termini. Among the above-mentioned oligomers, the polyether, aliphatic polyester, polylactone and polycarbonate are preferred because of high reactivity.
When the oligomer component (L) has a glass transition temperature over 20xc2x0 C., the decrease in the compatibility of the oligomer with the hydroxyl-terminated polymer (B) prevents the ester elastomer from attaining a sufficiently high degree of polymerization so that the strength of the elastomer may not be sufficient. The glass transition temperature is preferably not over 0xc2x0 C. and more preferably not higher than xe2x88x9220xc2x0 C.
When the oligomer component (L) has a number average molecular weight of less than 500, the block property of the polyester copolymer (A) is so low as to cause melting point depression, so that the mechanical strength of the ester elastomer will become insufficient. If 5000 is exceeded, the decrease in compatibility with the hydroxyl-terminated polymer (B) will prevent the ester elastomer from attaining a sufficient degree of polymerization so that the strength of the elastomer will be insufficient. The preferred range is 500 to 2000.
When the proportion of the short-chain polyester component (a1) is smaller than 50 weight %, the melting point of the polyester copolymer (A) is depressed to adversely affect the mechanical strength at high temperature of the ester elastomer. Conversely when said proportion exceeds 95 weight %, the resulting decrease in the compatibility with hydroxyl-terminated polymer (B) prevents the ester elastomer from attaining a sufficiently high degree of polymerization so that the strength of the elastomer will be insufficient. The preferred proportion of (a1) is 70 to 90 weight %.
The polyester copolymer (A) mentioned above can be obtained by reacting an aromatic dicarboxylic acid or an ester thereof, a low molecular weight diol, and said oligomer component (L). The oligomer component (L) forms said oligomer component (L) by the above reaction.
The aromatic dicarboxylic acid mentioned above includes but is not limited to terephthalic acid, isophthalic acid, orthophthalic acid, naphthalenedicarboxylic acid and p-phenylenedicarboxylic acid. The above-mentioned ester of aromatic dicarboxylic acid includes but is not limited to dimethyl terephthalate, dimethyl isophthalate, dimethyl orthophthalate, dimethyl naphthalenedicarboxylate and dimethyl p-phenylenedicarboxylate.
The low molecular weight diol mentioned above includes but is not limited to ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, 1,5-pentanediol and 1,6-hexanediol. Those diols can be used each independently or in a combination of two or more species.
The polyether (M) for use as said oligomer component (L) is preferably a polyether containing an alkylene group of 2 to 10 carbon atoms as represented by the following general formula (5),
xe2x80x94R6xe2x80x94Oxe2x80x94xe2x80x83xe2x80x83(5)
(wherein R6 represents an alkylene group of 2 to 10 carbon atoms). Thus, for example, polyethylene glycol, poly(1,3-propylene glycol), poly(1,2-propylene glycol), poly(tetramethylene glycol) and poly(hexamethylene glycol) can be mentioned. Among these compounds, poly(tetramethylene glycol) is particularly preferred from the standpoint of mechanical characteristics and weather resistance.
As said polyether, commercial products such as PTHF (manufactured by BASF) and PTMG (manufactured by Mitsubishi Chemical) can be used as they are.
The aliphatic polyester (N) for use as said oligomer component (L) is preferably a polyester having an alkylene group of 2 to 10 carbon atoms as represented by the following general formula (6).
xe2x80x94R7xe2x80x94Oxe2x80x94COxe2x80x94R8xe2x80x94COxe2x80x94Oxe2x80x94xe2x80x83xe2x80x83(6)
(where R7 and R8 each represents an alkylene group of 2 to 10 carbon atoms)
As said aliphatic polyester, commercial products such as Nippollan 4009, Nippollan 4010, Nippollan 4070 (manufactured by Nippon Polyurethane) can be utilized.
The polylactone (O) for use as said oligomer component (L) is preferably one obtainable by ring-opening polymerization of a lactone containing 3 to 11 carbon atoms as represented by the following general formula (7).
xe2x80x94R9xe2x80x94COxe2x80x94Oxe2x80x94xe2x80x83xe2x80x83(7)
(wherein R9 represents an alkylene group of 2 to 10 carbon atoms) Particularly preferred is a polymer of xcex5-caprolactone.
As a commercial product of said polylactone, TONE polyol (manufactured by Union Carbide), among others, can be mentioned.
The polycarbonate (P) for use as said oligomer component (L) may for example be a polycarbonate obtainable by ring-opening polymerization of an aliphatic carbonate containing 3 to 11 carbon atoms as represented by the following general formula (8).
xe2x80x94R10xe2x80x94Oxe2x80x94COxe2x80x94Oxe2x80x94xe2x80x83xe2x80x83(8)
(wherein R10 represents an alkylene group of 2 to 10 carbon atoms) Preferred are oligomers of propylene carbonate, tetramethylene carbonate and hexamethylene carbonate.
As a commercial product of the polycarbonate, Nippollan 981 (manufactured by Nippon Polyurethane), among others, can be mentioned.
The polyester copolymer (A) can be produced by the known polymerization procedures. A typical procedure comprises subjecting dimethyl terephthalate, said polyether and an excess of said low molecular weight diol to transesterification reaction under heating at 200xc2x0 C. in the presence of a catalyst and further to polycondensation reaction under reduced pressure at 240xc2x0 C. to provide a polyester copolymer (A). The copolymer (A) can also be produced in the like manner using said aliphatic polyester, polylactone, polycarbonate or the like in lieu of said polyether.
The instrinsic viscosity of said polyester copolymer (A) is preferably 0.05 to 1.0, more preferably 0.2 to 0.6. If the instrinsic viscosity is less than 0.05, the block property of the ester elastomer will be decreased to adversely affect the mechanical strength at high temperature. If, conversely, the instrinsic viscosity exceeds 1.0, the poor compatibility of copolymer (A) with hydroxyl-terminated polymer (B) prevents the ester elastomer from attaining a sufficient degree of polymerization, with the result the elastomer will have insufficient strength.
The instrinsic viscosity mentioned above means the viscosity value measured in the solvent o-chlorophenol at 25xc2x0 C.
The hydroxyl-terminated polymer (B) is a polymer having a glass transition temperature of not higher than 20xc2x0 C. and a number average molecular weight of 500 to 5000, with the absolute value of difference between the solubility parameter xcex4B of hydroxyl-terminated polymer (B) and the solubility parameter xcex4L of the oligomer component (L), i.e. |xcex4B-xcex4L| of not greater than 0.5.
The hydroxyl-terminated polymer (B) is not particularly restricted as far as it satisfies the above requirements. More particularly, a polyether, aliphatic polyester, polylactone, polycarbonate, polyolefin, polybutadiene, polyisoprene, polyacrylate, polysiloxane, etc. each having hydroxyl groups at both termini can be mentioned. Among them, a polyether (M), aliphatic polyester (N), polylactone (O), or polycarbonate (P) is preferred in view of its high reactivity.
The above-mentioned polyether (M), aliphatic polyester (N), polylactone (O) and polycarbonate (P) includes the same ones as mentioned for the oligomer component (L) hereinabove. It is preferred that the above-mentioned polymer (B) is as same as the oligomer component (L).
If the glass transition temperature of said hydroxyl-terminated polymer (B) exceeds 20xc2x0 C., the comparatibity of hydroxyl-terminated polymer (B) and polyester copolymer (A) is decreased to prevent the ester elastomer from attaining a sufficient degree of polymerization so that not only the strength of the elastomer will be inadequate but also the flexibility of the elastomer will be insufficient. The glass transition temperature of (B) is preferably not higher than 0xc2x0 C., more preferably not higher than xe2x88x9220xc2x0 C.
If the number average molecular weight of said hydroxyl-terminated polymer (B) is less than 500, the flexibility of the ester elastomer will be insufficient. If 5000 is exceeded, the elastomer will be excessively high in crystallinity so that its flexibility in the low temperature region will be poor. The preferred range of said number average weight is 500 to 3000 and the more preferred range is 500 to 1000.
It is necessary that the absolute value of difference between the solubility parameter xcex4B of hydroxyl-terminated polymer (B) and the solubility parameter xcex4L of the oligomer component (L), i.e. |xcex4B-xcex4L|, should be not greater than 0.5. The term xe2x80x9csolubility parameterxe2x80x9d as used herein means a value found applying solubility parameter of a solvent [(xcex94E/V)xc2xd] to a high polymer. Thus, xcex94E represents the molar vaporization energy of a solvent but in the case of a polymer, its molecular chain is fragmented into partial chains (segments) having substantially the same volumes as those of solvent molecules to postulate vaporatable units and the xcex94E is calculated by using the molar vaporization energy of each segment. In the above formula, V represents volume and, in this case, the volume of said segment. The solubility parameter is sometimes abbreviated as xcex4 value.
The above solubility parameter serves as an approximate indicator of the compatibility of a solvent and a high polymer, and further between a polymer and another polymer. In the present invention, as the hydroxyl-terminated polymer (B) and oligomer component (L) are selected so as to insure that said |xcex4B-xcex4L| will be 0.5 or less, the compatibility between hydroxyl-terminated polymer (B) and oligomer component (L) and, hence, the compatibility between hydroxyl-terminated polymer (B) and polyester copolymer (A) are improved, with the result that the reaction between them proceeds fast to provide an ester elastomer which is flexible and yet excellent in mechanical strength.
The solubility parameter of a polymer can be determined by the method described in Japanese Society of Polymer Chemistry (ed.): Polymer Data Book (1989, Baifu-kan, p. 592. In accordance with this method, a polymer is immersed in solvents having known solubility parameter xcex4S value and the solubility parameter of the polymer is calculated from the range of xcex4S values of the solvents which dissolve the polymer.
As methods for determining solubility parameters by computation, the method of Small and the method of Hoy are also known. The method of Hoy is described in Journal of the Adhesion Society of Japan, 22 (10), 564, 1986 and J. Paint Technology, 42, 76, 1970. In this method, the solubility parameter xcex4P of a polymer is calculated by means of the computation formula (1)
xcex4P=xcexa3F/Vxe2x80x83xe2x80x83(1)
where xcexa3F is a sum total of the corresponding values in Table 1 below for each recurring component of the polymer and the basal value given in Table 1, and is expressed in units of (cal/cm3)xc2xd/mol. In the above formula, V is a molar volume in units of cm3/mol, and from the molecular weight M and specific gravity d of each recurring unit of the polymer, the value of V is calculated by means of the following computation formula (2).
V=M/dxe2x80x83xe2x80x83(2)
A computation example for poly(tetrabutylene glycol), for instance, is shown below.
M=72.10
d=0.9346
xcexa3F=141.5xc3x974+114.98+135.1=816.08
V=72.10/0.9346=77.15
xcex4P=816.08/77.15=10.58
The ester elastomer comprising said polyester copolymer (A) and said hydroxyl-terminated polymer (B) which are coupled to each other through the intermediary of said urethane component (C) can be obtained by reacting the polyester copolymer (A) and the hydroxyl-terminated polymer (B) with an isocyanate compound (Cxe2x80x2).
When the terminal functional group of polyester copolymer (A) is hydroxyl, it is bound by an urethane component (C) of the following general formula (1). When the functional group is carboxyl, it is mainly bound by an urethane component (C) of the following general formula (2).
xe2x80x94Oxe2x80x94COxe2x80x94NHxe2x80x94R1xe2x80x94NHxe2x80x94COxe2x80x94Oxe2x80x94xe2x80x83xe2x80x83(1)
xe2x80x94Oxe2x80x94COxe2x80x94NHxe2x80x94R2xe2x80x94NHxe2x80x94COxe2x80x94xe2x80x83xe2x80x83(2)
The above general formulas (1) and (2) show the urethane component (C) derived from the isocyanate compound (Cxe2x80x2) having difunctional group(s), however it is preferable that the urethane component (C) contains a little amount of a component derived from a isocyanate compound (Cxe2x80x2) having tri- or polyfunctional group(s).
Referring to the above general formulas (1) and (2), R1 and R2 each represents an alkylene group of 2 to 15 carbon atoms, xe2x80x94C6H4xe2x80x94, xe2x80x94C6H4xe2x80x94CH2xe2x80x94, or xe2x80x94C6H4xe2x80x94CH2xe2x80x94C6H4xe2x80x94 (where xe2x80x94C6H4xe2x80x94 represents phenylene). R1 and R2 each may be an alkyl-substituted phenylene group or a combination of an alkylene group with a phenylene group. When the terminal group of the polyester copolymer (A) is carboxyl, it is considered that a minor proportion of molecules are bound by the urethane component of general formula (1) as well.
The above isocyanate compound (Cxe2x80x2) is not particularly restricted in structure as far as it contains two isocyanate groups within the molecule.
The isocyanate compound (Cxe2x80x2) mentioned above includes aromatic diisocyanates such as 4,4xe2x80x2-diphenylmethane diisocyanate, tolylene diisocyanate, phenylene diisocyanate, naphthalene diisocyanate, etc. and aliphatic diisocyanates such as 1,2-ethylene diisocyanate, 1,3-propylene diisocyanate, 1,4-butane diisocyanate, 1,6-hexamethylene diisocyanate, 1,4-cyclohexane diisocyanate, 1,3-cyclohexane diisocyanate, isophorone diisocyanate, hydrogenated 4,4xe2x80x2-diphenylmethane diisocyanate, etc.
It is preferable that the above-mentioned isocyanate compound (Cxe2x80x2) comprises a little amount of tri- and polyfunctional compounds, i.e. compounds having 3 or more isocyanate groups. The polyester elastomer resulting from the reaction with a polyisocyanate compound having 3 or more isocyanate groups is greater in molecular weight and gives a higher viscosity at melting state to improve moldability.
When said isocyanate compound (Cxe2x80x2) is partially replaced with a tri- or polyisocyanate compound, the average isocyanate number which is the total number of isocyanate groups in all the isocyanate compounds divided by the total number of the isocyanate compound is preferably not greater than 2.2. If the average isocyanate number exceeds 2.2, the viscosity at melting state will be too high so that the moldability is rather sacrificed. The above-mentioned isocyanate number of 2.2 corresponds to the use of, for example, a diisocyanate and a triisocyanate in a ratio of 4:1.
As the isocyanate compound having an average isocyanate number of 2 to 2.2, commercial products comprising mixtures of compounds having the different isocyanate number can be used. For example, Millionate MR200 (Product of Nippon Polyurethane Co.) is a mixture of compounds of the following general formula (9) wherein n=0, 1, 2, and more than 2, with an average isocyanate number of 2.8. In this invention, a commercial product of this type can be supplemented with a diisocyanate compound to give an overall average isocyanate number of not greater than 2.2.
OCNxe2x80x94[CH2xe2x80x94C6H3(NCO)]nxe2x80x94C6H4xe2x80x94NCOxe2x80x83xe2x80x83(9)
The polyester elastomer of the invention preferably comprises 100 parts by weight of polyester copolymer (A), 50 to 500 parts by weight of hydroxyl-terminated polymer (B), and 10 to 100 parts by weight of urethane component (C).
If the proportion of the hydroxyl-terminated polymer (B) is smaller than 50 parts by weight, the product polyester elastomer may not be sufficiently flexible, while the use of hydroxyl-terminated polymer (B) in excess of 500 parts weight will not provide for sufficient mechanical strength. The preferred range is 100 to 300 parts by weight.
If the proportion of urethane component (C) is smaller than 10 parts by weight, the ester elastomer cannot attain a sufficiently high degree of polymerization but will be low in mechanical strength. On the other hand, if 100 parts by weight is exceeded, the polyester elastomer will be of insufficient flexibility. The preferred range is 30 to 70 parts by weight.
The surface hardness of said ester elastomer is 60 to 90 and preferably 70 to 85. If a surface hardness is lower than 60, no sufficient mechanical strength will be attained. If 90 is exceeded, the ester elastomer will not be sufficiently flexible.
The surface hardness mentioned above can be measured in accordance with JIS K 6301 using Type A Spring at 23xc2x0 C.
The melting point of said ester elastomer is 170 to 230xc2x0 C., preferably 180 to 220xc2x0 C. When the melting point is below 170xc2x0 C., the mechanical strength at high temperature of the elastomer will be insufficient. If 230xc2x0 C. is exceeded, the moldability of the composition will be poor.
The melting point mentioned above can be determined by differential scanning calorimetry in terms of the endothermic peak owing to melting of crystals. The measurement is performed with an incremental temperature of 10xc2x0 C./min. and, as the instrument, T A Instruments"" xe2x80x9cDSC 2920xe2x80x9d, for instance, can be used.
The process for producing a polyester elastomer according to the second aspect of the invention comprises melt kneading 100 parts by weight of the polyester copolymer (A) composed of 50 to 95 weight % of the short-chain polyester component (a1) and 50 to 5 weight % of the long-chain polyester component (a2), the latter long-chain polyester component (a2) containing the oligomer component (L) having a glass transition temperature of not higher than 20xc2x0 C. and a number average molecular weight of 500 to 5000 as a constituent unit, 50 to 500 parts by weight of the hydroxyl-terminated polymer (B) having hydroxyl groups at both terminal ends, polymer B having a glass transition temperature of not higher than 20xc2x0 C. and a number average molecular weight of 500 to 5000, with the absolute difference |xcex4B-xcex4L| [wherein xcex4B represents the solubility parameter of the hydroxyl-terminated polymer (B) and xcex4L represents the solubility parameter of the oligomer component (L) in said long-chain polyester component (a2)] being not greater than 0.5, and 10 to 100 parts by weight of the isocyanate compound (Cxe2x80x2).
Preferably, the above process is carried out by melt kneading polyester copolymer (A) with polyether as the hydroxyl-terminated polymer (B) in the first place and then adding isocyanate compound (Cxe2x80x2). It is still more preferable to melt-knead polyester copolymer (A) with polyether as the hydroxyl-terminated polymer (B) and after a clear solution has been obtained, add the isocyanate compound (Cxe2x80x2).
If the amount of said hydroxyl-terminated polymer (B) is smaller than 50 parts by weight, the polyester elastomer will have insufficient flexibility. When it exceeds 500 parts by weight, sufficient mechanical strength will not be obtained. A preferred range is 100 to 300 parts by weight.
If the amount of said urethane component (C) is smaller than 10 parts by weight, the ester elastomer will not have a high molecular weight but will be low in mechanical strength.
If said amount is larger than 100 parts by weight, the polyester elastomer will be poor in flexibility. A preferred range is 30 to 70 parts by weight.
The amount of the isocyanate compound (Cxe2x80x2) is preferably such that the molar concentration [NCO] of isocyanate groups and the molar concentration [OH] of the sum of hydroxyl groups occurring in the polyester copolymer (A), the hydroxyl-terminated polymer (B), and another or other constituents, if any, have the following relation:
0.9 less than [NCO]/[OH] less than 1.2
If the ratio [NCO]/[OH] is lower than 0.9 or higher than 1.2, the stoichiometry of the reaction deviates excessively and a decreased molecular weight and insufficient mechanical strength will result.
In cases where an amine compound, which is to be mentioned later herein, is used, the total molar concentration ([OH]+[NH2]+[NH]) should be used in lieu of the molar concentration [OH] of hydroxyl groups in the above relation.
The above-mentioned polyester copolymer (A), the hydroxyl-terminated polymer (B) and the isocyanate compound (Cxe2x80x2) can be subjected to reaction by melt kneading using an extruder. The extrusion temperature is preferably 180 to 260xc2x0 C., more preferably 200 to 240xc2x0 C. At an extrusion temperature lower than 180xc2x0 C., the reaction will be difficult to conduct since the polyester copolymer (A) will not melt, making it impossible to obtain a high molecular weight polymer. At a temperature above 260xc2x0 C., the polyester copolymer (A) and isocyanate compound (Cxe2x80x2) tend to decompose, hence a polymer having sufficient strength will be unobtainable.
Said extruder is not particularly restricted. Thus, for example, a single-screw or twin-screw extruder may be used. Among them, a twin-screw extruder with the two screws rotating in the same direction or in opposite directions is preferred because of better agitating/mixing efficiency. A twin-screw extruder with the two screws rotating in the same direction and engaging with each other is more preferred.
By adding a compound having two or more reactive functional groups within the molecule to the above-mentioned polyester copolymer (A), the hydroxyl-terminated polymer (B) and the diisocyanate compound (Cxe2x80x2) on the occasion of the reaction, it is possible to increase the molecular weight of the resulting elastomer and improve the moldability and bending resistance thereof.
The reactive functional groups mentioned above include epoxy, hydroxyl, and hydrogen groups constituting Nxe2x80x94H bond, among others. As compounds having such functional groups, there may be mentioned polyfunctional epoxy compounds, polyfunctional alcohol compounds, amine compounds having one or more amino groups, amine compounds having one or more imino groups, compounds having at least one epoxy group and at least one hydroxyl group within the molecule, and compounds having at least one epoxy group and at least one amino group within the molecule, among others.
The compounds having two or more reactive functional groups such as mentioned above may be used in combination of two or more kinds. In particular, the combined use of a polyfunctional epoxy compound and a polyfunctional amine compound is preferred.
In cases where a compound having two or more reactive functional groups such as mentioned above is used, it is preferred that after melt kneading of the polyester copolymer (A), the hydroxyl-terminated polymer (B) and the diisocyanate compound (Cxe2x80x2), said compound having two or more reactive functional groups be added and the whole be melt-kneaded. If, for instance, the four components, namely the polyester copolymer (A), the hydroxyl-terminated polymer (B), the isocyanate compound (C) and epoxy compound, are fed simultaneously for melt kneading, the reaction will proceed heterogeneously due to the differences in reactivity of the polyester copolymer (A), the hydroxyl-terminated polymer (B) and epoxy compound with the isocyanate compound (C), failing to give an elastomer showing sufficient mechanical strength. Similarly, the procedure comprising melt-kneading the polyester copolymer (A), the hydroxyl-terminated polymer (B) and the epoxy compound, then feeding the isocyanate compound (Cxe2x80x2), and melt kneading will fail to give an elastomer showing sufficient mechanical strength.
The above-mentioned compound having two or more reactive functional groups is preferably added in an amount of 0.01 to 20 parts by weight per 100 parts by weight of the polyester copolymer (A). At an addition amount below 0.01 part by weight, the obtained polyester elastomer will be unable to acquire a sufficient viscosity at melting state. At an amount exceeding 20 parts by weight, gelation may proceed, resulting in loss of melt fluidity in some instances. A preferred range is 0.1 to 10 parts by weight.
The polyfunctional epoxy compound to be used in the practice of the present invention includes polyphenol type, polyglycidylamine type, alcohol type, ester type, and alicyclic type ones, among others. Specifically, there may be mentioned bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, glycerol polyglycidyl ether, ethylene or polyethylene glycol diglycidyl ether, pentaerythritol polyglycidyl ether, N,Nxe2x80x2-diglycidylphenylaniline, N,N,Nxe2x80x2,Nxe2x80x2-tetraglycidyldiaminodiphenylmethane, hydrogenated phthalic acid diglycidyl ester, phthalic acid diglycidyl ester, 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate, and the like. As commercial products, there may be mentioned, for example, Nagase Kasei""s xe2x80x9cDenacolxe2x80x9d, Ciba-Geigy""s xe2x80x9cAralditexe2x80x9d, and Yuka-Shell-Epoxy""s xe2x80x9cEpikotexe2x80x9d. Two or more of these may be used combinedly.
The polyfunctional alcohol compound to be used in the practice of the present invention includes, among others, diols such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, 1,5-pentanediol and 1,6-hexanediol, triols such as trimethylolpropane and glycerol and, further, alcohols having four or more hydroxyl groups within the molecule, such as pentaerythritol. Two or more of these may be used combinedly.
The amine compound to be used in the present invention may be any one provided that it has two or more nitrogen-bound hydrogen atoms. As such compound, there may be mentioned compounds having one or more amino groups, compounds having two or more imino groups, compounds having a total of two or more of amino and imino groups combinedly. Specifically, there may be mentioned aniline, ethylenediamine, hexamethylenediamine, phenylenediamine, diaminodiphenylmethane, diaminodiphenyl sulfone, diethylenetriamine, diethylaminopropylamine, and the like. Two or more of these may be used combinedly.
In the practice of the present invention, a catalyst may be used in the step of melt kneading the polyester copolymer (A) and the hydroxyl-terminated polymer (B) with the isocyanate compound (Cxe2x80x2).
As said catalyst, there may be mentioned, for example, diacyltin (II), tetraacyltin (IV), dibutyltin oxide, dibutyltin dilaurate, dimethyltin maleate, tin dioctanoate, tin tetraacetate, triethyleneamine, diethyleneamine, triethylamine, naphthenic acid metal salts, octylic acid metal salts, triisobutylaluminum, tetrabutyl titanate, calcium acetate, germanium dioxide, antimony trioxide, and the like. These may be used singly or two or more of them may be used in combination.
The above-mentioned ester elastomer may contain a stabilizer. Said stabilizer includes, among others, hindered phenolic antioxidants such as 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene, and 3,9-bis[2-[3-(3-t-butyl-4-hydroxy-5-methylphenyl)-propionyloxy]-1,1-dimethyl-ethyl]-2,4,8,10-tetraoxaspiro[5.5]undecane; heat stabilizers such as tris(2,4-di-t-butylphenyl)phosphite, trilauryl phosphite, 2-t-butyl-xcex1-(3-t-butyl-4-hydroxyphenyl)-p-cumenylbis(p-nonylphenyl)phosphite, dimyristyl 3,3xe2x80x2-thiodipropionate, distearyl 3,3xe2x80x2-thiodipropionate, pentaerythrityl tetrakis(3-laurylthiopropionate) and ditridecyl 3,3xe2x80x2-thiodipropionate; and the like.
In the process of producing the ester elastomer of the present invention or after the production thereof, an additive or additives selected from among fibers, inorganic fillers, flame retardants, ultraviolet absorbers, antistatic agents, inorganic materials, higher fatty acid salts and the like may be added at amounts at which the practical value of said elastomer will not be impaired.
The fibers mentioned above include, among others, inorganic fibers such as glass fiber, carbon fiber, boron fiber, silicon carbide fiber, alumina fiber, amorphous fiber silicon fiber, titanium fiber, carbon fiber, and organic fibers such as aramid fiber and the like.
The inorganic fillers mentioned above include, among others, calcium carbonate, titanium oxide, mica, talc and the like. The flame retardants mentioned above include, among others, hexabromocyclododecane, tris-(2,3-dichloropropyl)phosphate, pentabromophenyl allyl ether and the like.
The ultraviolet absorbers mentioned above include, among others, p-tert-butylphenyl salicylate, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-methoxy-2xe2x80x2-carboxybenzophenone, 2,4,5-trihydroxybutyrophenone and the like.
The antistatic agents mentioned above include, among others, N,N-bis(hydroxyethyl)alkylamines, alkylarylsulfonates, alkylsulfonates and the like. The inorganic materials mentioned above include, among others, barium sulfate, alumina, silicon oxide and the like. The higher fatty acid salts mentioned above include, among others, sodium stearate, barium stearate, sodium palmitate and the like.
The properties of the ester elastomer of the present invention may further be modified by incorporating another thermoplastic resin and/or a rubber component.
As said thermoplastic resin, there may be mentioned, for example, polyolefins, modified polyolefins, polystyrene, polyvinyl chloride, polyamides, polycarbonates, polysulfones and polyesters.
The rubber component mentioned above includes, among others, natural rubber species, styrene-butadiene copolymers, polybutadiene, polyisoprene, acrylonitrile-butadiene copolymers, ethylene-propylene copolymers (EPM, EPDM), polychloroprene, butyl rubbers, acrylic rubbers, silicone rubbers, urethane rubbers, olefin-based thermoplastic elastomers, styrenic thermoplastic elastomers, vinyl chloride-based thermoplastic elastomers, ester-type thermoplastic elastomers, amide-type thermoplastic elastomers and the like.
The ester elastomer of the present invention can be formed into moldings by molding techniques in general use, such as press molding, extrusion molding, injection molding and blow molding. The molding temperature may vary depending on the melting point of the ester elastomer and on the molding technique employed but suitably lies within the range of 160 to 260xc2x0 C. If the molding temperature is below 160xc2x0 C., the ester elastomer will show low fluidity and therefore uniform moldings may not be obtained. At a temperature above 260xc2x0 C., the ester elastomer will undergo decomposition, failing to give ester elastomer moldings with sufficient strength.
The moldings obtained by using the ester elastomer of the present invention are suitably used as automotive parts, electric or electronic parts, industrial parts, etc. or in sports equipment or sporting goods, medical equipment or products, for instance.
The automotive parts include, among others, boots such as constant velocity joint boots and rack-and-pinion boot; ball joint seals; safety belt parts; bumper fascias; emblems; braids; and the like.
The electric or electronic parts include, among others, wire coverings, gears, rubber switches, membrane switches, tact switches, O rings, and the like.
The industrial parts include, among others, hydraulic hoses, coil tubes, sealing members, packings, V belts, rolls, damping or vibration-reducing materials, shock absorbers, couplings, diaphragms, and the like.
The sporting goods include, among others, shoe soles, balls for ball games, and the like.
The medical goods include, among others, medical tubes, blood transfusion packs, catheters, and the like.
In addition to the above applications, the elastomer can suitably be used also in producing elastic fibers, elastic sheets, composite sheets, and hot melt adhesives, or as a material for preparing alloys with other resins.
The ester elastomer of the present invention can simultaneously satisfy those requirements imposed with respect to flexibility and mechanical strength, in particular mechanical strength at high temperature, which the so-far known ester copolymers cannot meet.
Thus, the ester elastomer according to the third aspect of the present invention is characterized in that it has a surface hardness of 60 to 90 and a compression set of not more than 90% as measured after 72 hours of compression at 120xc2x0 C.
This ester elastomer has ideal performance characteristics as a thermoplastic elastomer.
Said surface hardness is measured at 23xc2x0 C. using an A-type spring according to JIS K 6301.
If the surface hardness is lower than 60, the mechanical strength will be poor, hence the durability will be insufficient. If said hardness is above 90, the flexibility will be poor, hence the use as an elastic material will become difficult. The surface hardness is preferably within the range of 80 to 89, more preferably 85 to 89.
If the compression set after 72 hours of compression at 120xc2x0 C. exceeds 90%, the creep resistance will be low, hence durability problems will arise. In applications where the elasticity of the elastomer is utilized for sealing purposes, for instance, the elastomer, after repeated deformation, will no more show the original elasticity, whereby troubles may arise. It is more preferred that said compression set be not more than 85%.
Preferred examples of the ester elastomer having a surface hardness of 60 to 90 and a compression set of not more than 90% as measured after 72 hours of compression at 120xc2x0 C. are block copolymers composed of an aromatic polyester and a polyether. Such block copolymers comprising an aromatic polyester and a polyether can be obtained by selecting a polyether as the oligomer component (L) and as the hydroxyl-terminated polymer (B) in the ester elastomer mentioned above.
In addition, it is preferred that the ester elastomer have a melting point of 170 to 230xc2x0 C. as measured by differential scanning calorimetry. The melting point mentioned above can be determined by differential scanning calorimetry in terms of the endothermic peak owing to melting of crystals. The measurement is performed with an incremental temperature of 10xc2x0 C./min. and, as the instrument, T A Instruments"" xe2x80x9cDSC 2920xe2x80x9d, for instance, can be used.
That said aromatic polyester- and polyether-based block copolymer has a melting point of 170 to 230xc2x0 C. as measured by differential scanning calorimetry means that the aromatic polyester block chain length is longer as compared with the conventional ones, and this structure is conducive to simultaneous realization of the above-mentioned surface hardness and compression set at 120xc2x0 C. If the melting point is below 170xc2x0 C., the aromatic polyester block chain length will be short, allowing the compression set to exceed 90%, hence the physical properties at high temperature will be poor. If the melting point is higher than 230xc2x0 C., it will be difficult to use the copolymer as a flexible material.
It is preferred that the aromatic polyester in the ester elastomer having a surface hardness of 60 to 90 and a compression set of not more than 90% after 72 hours of compression at 120xc2x0 C. be polybutylene naphthalate or polyethylene naphthalate. Polyester elastomers containing polybutylene naphthalate or polyethylene naphthalate within their structure are excellent in physical properties at high temperature and satisfy the above-mentioned compression set requirement.
The short-chain polyester component (a1) in the ester elastomer of the present invention serves as a hard segment, and crystals formed by this component form crosslinking sites, while the oligomer component (L) and hydroxyl-terminated polymer (B) serve as soft segments, showing entropy elasticity, whereby the characteristics as an elastomer can be exhibited.
In the so-far known ester elastomers, an increase in soft segment proportion for attaining flexibility unavoidably results in a reduction in hard segment length, hence in a lowered melting point and poor mechanical properties at high temperature. On the contrary, in the present invention, according to which a block copolymer is preliminarily prepared from the short-chain polyester component (a1) and the oligomer component (L)xe2x80x94containing long-chain polyester component (a2) and then it is subjected to chain elongation reaction with the hydroxyl-terminated polymer (B), each of the respective components shows its feature as a block to a high extent, so that a high melting point can be realized and at the same time a polyester elastomer excellent in flexibility and physical properties at high temperature can be provided.
In addition, owing to the presence of the short-chain polyester component (a1) mentioned above, the ester elastomer of the present invention tends to crystallize more easily than the so-far known ester elastomers showing the same degree of flexibility and, as a result, sites of firm crosslinking are formed, providing an elastomer material excellent in mechanical characteristics at high temperature. Furthermore, the presence of the oligomer component (L) and hydroxyl-terminated polymer (B) as block chains contributes to an increase in molecular weight between crosslinking sites. As a result, there is provided an elastomer material rich in flexibility.